1. Field of the Invention
Methods and apparatuses consistent with the relate to capturing still images of high image quality at high speed.
2. Description of the Related Art
As electronic engineering has been developed, various devices for obtaining image data of high image quality have been widely distributed. For example, professional image input apparatuses such as portable digital cameras and camcorders, camera phones and personal digital assistances (PDAs) having built in cameras are widely used. In the image input apparatus, photons passing through an optical system are converted into electric signals by an image sensor, and the electric signals are converted into various image formats through an image processor.
Personal image input apparatuses have been greatly developed. A few years ago, digital cameras provided images with only two to three mega-pixels. However, digital cameras providing image data of ten mega-pixels or more are now widely used, and are being used instead of conventional analog cameras. Moreover, Internet blogs are being widely used, and thus, general users can share their own image data on Internet.
Recent image input apparatuses provide functions for compression of and reproducing of moving pictures and still images. For example, digital camcorders compress moving picture information using a moving picture codec, store the compressed moving picture data in an external recording apparatus such as an external memory, a tape, or a hard disk drive (HDD), and reproduce the moving picture data. In addition, digital camcorders can compress, store, and recover still images as well as moving pictures. Digital cameras can compress, store, and reproduce still images of high resolution, and can also compress, store, and reproduce moving pictures.
However, as image input apparatuses become more widely distributed, demands placed on image input apparatuses by users increase. Recently, the use of digital single lens reflex (DSLR) cameras that are for professional usage in order to obtain images of high image quality is increasing, and thus, the center of the camera market is moving toward DSLR cameras from high-end cameras. The user can realize various effects on pictures using the DSLR camera. For example, the user can take a picture of his/her favorite athlete from a far distance using a high-magnification lens, and pictures of celestial constellations with a long exposure time. Moreover, fantastic night views can be photographed using various filters such as a cross filter. In addition, moving subjects, for example, moving cars, athletes during a game, and babies, are photographed using a successive capturing function of the camera.
The successive capturing function is for photographing a subject moving at high speed a plurality of times within a short period of time. The successive capturing function is used when a moving subject is to be photographed, and also used when a subject is photographed successively in order to pick favorite pictures among the successive pictures.
FIG. 1 is a block diagram illustrating a successive capturing method using an image input apparatus according to the related art.
The image data captured by an image sensor 210 is stored in an internal memory 220 after passing through an image signal processor 250, a pre-processor 255, and a data bus 240. The image data is encoded by a still image codec 260 and stored in the internal memory 220 again, and if necessary, the image data is also stored in an external memory 230. The encoded image data is provided to a display unit 290 through a post-processor 275.
However, there is a problem in the successive capturing method used in the related art. Elements for determining the capture speed are as follows. First, the successive capture speed is determined according to a processing time of the image sensor, the size of the image data, and the resolution. Second, the time taken for compressing and reproducing the image data determines the successive capture speed, and then, a write speed of the external memory that can store the successively captured bit streams can determine the successive capture speed. The successive capture speed denotes the number of successive pictures that can be taken within a predetermined period of time, and generally, denotes the number of pictures taken per second. Among the above elements, the image capturing, the processing time of the image signal processor, and a JPEG encoding operation can be sped up by developments in semiconductor technology, and thus, the successive capture speed can be improved. However, an access speed to the external memory is slower than that of the internal memory, and thus, due to the slow access speed, a bottleneck phenomenon can happen. Therefore, there is a limitation in improving the successive capture speed due to the slow write speed of the external memory that stores the compressed JPEG files.
FIG. 2 is a series of photographs showing results of the successive capturing method according to the related art.
Referring to FIG. 2, when a subject who is continuously moving is photographed, a lot of the movements of the subject are lost because the successive capture speed is slow. For example, when an athlete running a marathon reaches the finish line and the athlete is successively captured, the most important shot of the athlete at the finish line, might not be captured. In addition, if a baby who cannot control his/her body by itself is successively captured, it is difficult to obtain natural images of the baby, such as the baby closing his/her eyes. Referring to FIG. 2, the movements of the subject performing a ballet are photographed unnaturally because the successive capture speed is slow.
Another problem of the related art successive capturing method is related to the external memory. If the images are successively captured by a few frames, for example, tens of frames per second, each of the frames that is compressed using a still image codec (for example, motion JPEG (M-JPEG)) is stored as an independent file. However, not all of the frames that are successively captured are effective, and the user selects a favorite one among the tens of frames. Then, the remaining tens of frames are stored in the external memory and deleted later. In this process, the frequent read/write operations of the external memory can reduce the lifespan of the external memory. Moreover, since the image data, most of which is to be deleted, is stored in the external memory, the external memory having a large capacity is required.
Therefore, a technology for reducing the amount of image data stored in the external memory while improving the successive capture speed in the digital image input apparatus is required.